1. Field of the Invention and Related Art
The present invention relates to a control apparatus for a vibration type actuator, such as a vibration wave motor or the like.
2. Related Background Art
Generally, a vibration type actuator, such as a vibration wave motor or the like, includes a vibration member for making driving vibration and a contact member for press contacting the vibration member, whereby the driving vibration causes the vibration member and the contact member to move relative to one another.
The vibration member generally consists of an elastic member and a piezoelectric element functioning as an electro-mechanical energy conversion element. For example, the piezoelectric element may be disposed so as to have driving phases at positions having spatially a mutual phase difference of 90xc2x0 for each driving phase of the elastic member, wherein alternating signals of two phases having a mutual phase difference of 90xc2x0 are applied to these two driving phases to generate a travelling wave on the elastic member, and the contact member is press-contacted with the elastic member, thereby obtaining a frictional driving force therebetween.
A frictional material for obtaining the appropriate frictional force is adhered, coated or formed at the contact portion between the vibration member and the contact member.
When compared with an actuator using electromagnetic force, the driving torque of a vibration type actuator at low speed is large, responsiveness is excellent, and it is silent because a vibration above the human audible range is used, so humans do not sense any driving sound is generated. Therefore, the vibration type actuator is suitably used as, e.g., the driving unit of an image formation apparatus.
Generally, since a large voltage is necessary for a vibration type actuator, the voltage is boosted or raised by one method or a combination of plural methods. For example, a driving signal may be amplified by a linear amplifier, the voltage may be boosted by a transformer, or an inductance element and a switching element may be combined such that a resonance with the capacitance component of the vibration type actuator may be used.
In these methods described above, either the method of boosting the voltage using a transformer or the method of boosting the voltage using a combination of an inductance element and a switching element is desirably used because each is excellent in respects of efficiency, costs and the like.
Moreover, as methods of controlling the driving speed of the vibration type actuator, there are a method of controlling the driving speed using a driving voltage, a method of controlling the driving speed using a driving frequency, and a method of controlling the driving speed using a phase between adjacent driving phases. Of these methods, the method of controlling the driving speed using the driving frequency is desirably used because it can achieve both a wide dynamic range and high resolution alone, and is excellent when used with a recently developed digital circuit.
However, in the driving speed control method using the driving frequency, as shown in FIG. 4, a frequency-speed characteristic changes greatly according to the frequency, whereby there is a problem in that a change rate of the speed varies even at the same control operation amount.
Particularly, if the driving frequency is displaced from a resonance frequency (fr), a slope (i.e., the slope of the frequency curve for the speed) decreases, whereby there is a problem in that a necessary control gain can not be obtained and the speed does not decrease.
That is, there is a problem that controllability deteriorates in a low-speed range. Further, if the control gain is set at low speed, there is a problem in that oscillation occurs in high-speed driving. Particularly, when the vibration type actuator is used in positioning control, there is a problem in that a desired device can not be accurately stopped at a desired position.
An object of the present invention is to provide a control apparatus, for a vibration type actuator, which achieves steady driving by a simple manner in a wide range of the driving from high speed to low speed.
In one aspect, the present invention relates to a control apparatus and method for a vibration type actuator which makes driving vibration at a driving unit of a vibration member by applying an alternating signal to an electro-mechanical energy conversion element and uses at least a frequency of the alternating signal as a speed control parameter, where the apparatus comprises: a driving circuit capable of changing a driving voltage of the alternating signal to be applied to the electro-mechanical energy conversion element; and a control circuit for controlling the driving circuit so that at least an absolute value of a slope of a frequency-speed characteristic of the actuator is within a predetermined range in a frequency band of predetermined range.
In another aspect, the present invention relates to a control apparatus and method for a vibration type actuator which makes driving vibration at a driving unit of a vibration member by applying an alternating signal to an electro-mechanical energy conversion element and uses at least a frequency of the alternating signal as a speed control parameter, where the apparatus comprises: a driving circuit capable of changing a driving voltage of the alternating signal to be applied to the electro-mechanical energy conversion element; and a control circuit for controlling the driving circuit so that an absolute value of a slope of a frequency-speed characteristic of the actuator is a predetermined value or greater at least in a frequency band of predetermined range.
In another aspect, the present invention relates to a control apparatus and method for a vibration type actuator which makes driving vibration at a driving unit of a vibration member by applying an alternating signal to an electro-mechanical energy conversion element and controls at least a frequency of an alternating signal as a speed control parameter, where the apparatus comprises: a driving circuit capable of changing a driving voltage of the alternating signal to be applied to the electro-mechanical energy conversion element; and a control circuit for at least performing control in a frequency range higher than a predetermined frequency so that the driving voltage to be applied to the electro-mechanical energy conversion element by the driving circuit decreases as the predetermined frequency becomes a higher frequency.
Other objects of the invention will become apparent from the following embodiments which will be explained with reference to the attached drawings.